This invention relates generally to computer systems and more particularly to clustered computer systems.
As is known in the art, a computer system is generally comprised of a central processing unit (CPU), a memory unit, at least one input/output device, and a bus which is used to connect the aforementioned devices. The computer is housed in a cabinet which contains a power supply to supply power for the various components of the computer. In operation, the central processing unit fetches and decodes incoming instructions, executes commands, and manipulates data, while the memory unit, which is composed of multiple storage locations, stores data to be used by the CPU. The I/O device is generally used to input data to and output data from the computer system. Typical types of I/O devices include printers, keyboards, displays and mass storage units such as disk drives etc. These devices are often interfaced to the computer system with an I/O interface controller circuit.
Often, a user's processing needs will grow beyond the capabilities of a single CPU. In an effort to meet these new processing needs, computers are typically clustered to make a plurality of CPUs available for processing. A clustered computer system is an integrated group of computers that communicate over a high-speed communication path. The clustered computer system acts as a single system to users. That is, clustered computer systems are characterized by a high degree of transparent resource sharing, which includes access by each individual computer system to storage located anywhere in the clustered system, and increased processing throughput.
In a typical cluster, there are two or more CPUs sharing inter alia at least one common system disk. Using multiple CPUs in a clustered configuration enables processing time on the CPUs to be used more efficiently. Thus, it affords the user better performance when jobs are run on a clustered system.
At least one additional general purpose computer is necessary to provide a clustered configuration for a computer system. Depending upon the characteristics of an existing system it may be possible to acquire an additional CPU and associated cabinet and power supply and interconnect these devices with the existing equipment. The two systems are connected through the additional cables and harnessing and are configured using software to behave as a clustered computer system. While the existing equipment and acquired general purpose computer system will provide a clustered computer system there are several drawbacks to this approach. For example, included with each general purpose computer system is a power supply and the cabinet as well as additional hardware such as cables and harnessing to connect the two computer systems. Clustering computer systems using this approach provides a redundancy in the hardware of the computer system, but at a substantial increase in cost particularly for the mechanical components necessary to provide the clustered system. Moreover, by providing separate cabinets, longer cables and harnesses are needed to interconnect the systems. This limits the maximum number of systems which can be interconnected, particularly for executing bus specification protocols, due to electrical timing and parameter considerations.
Another option available to provide additional processing power is multiprocessing. A single processing board can be used which includes multiple CPUs. This option however is not only costly but it assumes the user has foreseen a future need for an increase in processing power.